Apparatus for continuously casting steel

ABSTRACT

The tundish-to-mold stream in a continuous casting apparatus is provided with an inert, protective atmosphere and aluminum wire is introduced into the steel by means of a feed tube mounted in the mold. The wire is fed to the region at which the tundish-tomold stream joins the pool of molten metal in the mold. The rate of aluminum feed is controlled to introduce from 0.01 - 0.08 percent aluminum and the chemistry of the steel is controlled to provide from 0.010 - 0.025 percent sulfur and a detectable amount of calcium in solution. The non-metallic inclusions resulting are of globular, small size, in the range of 1-3 microns and are oxysulfides of aluminum, calcium and manganese.

United States Patent [191 Bunting, Jr. et al.

[ Oct. 23, 1973 APPARATUS FOR CONTINUOUSLY CASTING STEEL [75] Inventors:Robert L. Bunting, Jr., Wanakah;

Theodore C. Ring, Dunkirk; Joseph DAmato; Witold M. Wojcik, both ofFredonia, all of NY.

[73] Assignee: Roblin Industries, Inc., Buffalo,

fz ii' i iiiiT sIfiil 4, 1969 [21] Appl. No.: 855,119

[52] U.S. C1. 164/66, 164/281, 164/275, 164/273, 164/83 [51] Int. ClB22d 21/02, B22d 23/00 [58] Field of Search 164/57, 56, 55, 281,164/275, 66, 266, 82, 83

[56] References Cited UNITED STATES PATENTS 3,331,680 7/1967 Leupold164/56 X 3,465,811 9/1969 De Castelet 164/281 3,459,537 8/1969 Homak164/82 3,451,594 6/1969 Stewart 164/259 X 3,315,323 4/1967 Speith et al164/82 Primary Examiner--J. Spencer Overholser Assistant Examiner--V. K.Rising Attorney-Bean and Bean [5 7] ABSTRACT The tundish-to-mold streamin a continuous casting apparatus is provided with an inert, protectiveatmosphere and aluminum wire is introduced into the steel by means of afeed tube mounted in the mold. The wire is fed to the region at whichthe tundish-to-mold stream joins the pool of molten metal in the mold.The rate of aluminum feed is controlled to introduce from 0.01 0.08percent aluminum and the chemistry of the steel is controlled to providefrom 0.010 0.025

percent sulfur and a detectable amount of calcium in solution. Thenon-metallic inclusions resulting are of globular, small size, in therange of l-3 microns and are oxy-sulfides of aluminum, calcium andmanganese.

1 Claim, 3 Drawing Figures PAIENIEMBI23 ma 3.766661 FIG. I

2 INVENTORS ROBERT L. HUNTING, JR. THEODORE c. RING JOSEPH D'AMATOWITOLD M. WOJCIK MZM ATTORNEYS APPARATUS FOR CONTINUOUSLY CASTING STEELBACKGROUND OF THE INVENTION The continuous casting of steel is more andmore becoming a commercially important source of steel used in thefabrication of various finished or semi-finished products. Regardless ofthe process for producing it, a major source of concern in the steelmaking industry is the nature and size of the non-metallic inclusionswhich inevitably occur as a result of the process used. lngot caststeels, because the ingots are of large initial cross section normallyare subjected to considerable reduction in cross sectional area and thenon-metallic inclusions the-rein are likewise reduced in section andsubstantially elongated in the resultant product. Continuous caststeels, on the other hand, usually are of relatively small cross sectionand may be subjected, at most, to very little reduction in crosssectional area. As a result, the non-metallic inclusions in continuouslycast steel usually remain less deformed and less reduced in their crosssections than those in ingot steel, i.e., they might remain larger thanwould be desirable for a particular finsihed or semi-finished product.

For this reason, the commercial application of continuously cast steelsis often limited because of the aforesaid non-metallic inclusions.

BRIEF SUMMARY OF THE INVENTION Copending application Ser. No. 745,728,filed July 18, 1968, discloses method and apparatus for controlling thesize and distribution of non-metallic inclusions in continuously caststeels. The present invention is an adjunct to such disclosure in thatit employs the use of an inert atmosphere containing the tundish-to-moldstream. Additionally, the present invention incorporates the controlledintroduction of aluminum directed to the steel cast into the mold, andthe chemical control of the steel so that the inevitable non-metallicinclusions are'present in extremely small size and of such chemicalnature as most advantageously affects the quality of the steel.

The present invention, in particular, relates to the continuous castingof AISI carbon and low alloy steels.

More particularly, the present invention relates to such steels in whichthe non-metallic inclusions are in the form of oxy-sulfide globuleswhich are very hard, of small size in the order of 1-3 microns, and areconsequently of such shape, size and hardness as will not be altered byrolling, etc.

An object of this invention is to provide method and apparatus forcontinuously casting high quality and commerically important AISI carbonand low alloy steels.

Another object of this invention is to provide such steels with a finegrain structure consisting of Mac- Quaid grain size of at least 5.MacQuaid grain size" is obtained by subjecting the metal to the testinstituted by MacQuaid and which is defined for example by theconditions fixed by the standard E.l9-33 of the American Society forTesting Materials.

BRIEF DESCRIPTION OF THE DRAWING FIGURES FIG. 1 is a vertical sectiontaken through a continuous casting assembly, showing portions thereofand illustrating the apparatus for introducing aluminum directly to themold;

FIG. 2 is an enlarged section showing the introduction of the aluminumwire; and

FIG. 3 is a perspective view of the plate for accommodating the tube forintroducing the aluminum wire.

DETAILED DESCRIPTION OF THE INVENTION With reference to FIG. 1,reference character 10 indicates the ladle containing a body 12 ofmolten steel, the bottom 14 of the ladle being provided with a nozzle 16through which a stream 18 of molten steel is directed to the tundishindicated generally by the reference character 20. It will beunderstood, of course, that the usual stopper rod is associated with thenozzle 16 to allow the ladle operator to maintain the level of moltensteel 22 in the tundish at some predetermined level. The tundishassembly 20, the molds 24 and 26 and the shrouding 28 and 30 extendingbetween the bottom 32 of the tundish 20 and the top surface of the molds24 and 26 are described in the above mentioned copending application andrequire no further description, the disclosure of the copendingapplication being incorporated herein by reference.

Suffice it to say that the vertically reciprocating molds 24 and 26 arecooperatively related to the shrouds 28 and 30 such as continuously toshroud and contain the tundish-to-mold streams 34 and 36 emanating fromthe nozzles 38 and 40 in the bottom of the tundish and that suitablemeans including the inlet pipes 42 and 44 are provided to introduce aninert atmosphere within the shrouds in the manner described and for thepurposes set forth in the copending application.

The present invention incorporates a base plate indicated generally bythe reference character 46 in FIG. 3 which is provided with a centralopening 48 for registry with the opening in the respective mold 24 or 26minum to continuously cast steels creates special problems, particularlythe problem of alumina bridging across and closing the tundish nozzles38 and 40. Attempts have been made to introduce aluminum into thetundish-tomold stream but uniformly have met with disastrous resultsbecause of the tendency for the aluminum wire to be deflected so that itis not uniformly melted and uniformly introduced into the steel.

The present invention is particularly directed to the feature ofmounting the tube 52 or the guide for introducing the aluminum wiredirectly on the reciprocating mold in question so that the wire moves upand down with the mold and may be introduced continuously at anadvantageous point whereat the rate of introduction of aluminum into thesteel may be closely controlled so that the amount of aluminum sointroduced is within predetermined limits. As will hereinafter bepointed out, the amount of aluminum introduced is an importantconsideration.

Leading to the guide tube 52 is a flexible tube 60 anchored as at 62 toa suitable support 64 which contains a feeding roller 66 andpressure-producing idler rollers 68, the roller 66 being driven by asuitable electric motor 70 whose rotational speed is closely controlledto withdraw the aluminum wire from the supply roll 72 thereof at apredetermined rate related to the casting rate of the mold in question.The support 64 includes the spindle 74 for mounting the supply roll 72.

The support plate is mounted externally on a suitable rigid portion ofthe framework supporting the casting assembly and the flexible tubeportion 60 accommodates readily for the vertical reciprocatory motionsof the associated molds 24 and 26. The interiors of the shrouds 28 and30 are maintained under slight positive pressure so that there is a slowbleed off of inert gas such as argon through the tubes 52 and 60 such aswill positively preclude the introduction of air or oxygenrich gas intothe interiors of the shroud assemblies 28 and 30.

The desideratum of the present invention is to avoid the formation ofundesirable exogenous non-metallic inclusions which are silicates andalumina. The steels with which this invention is concerned contain bothmanganese and silicon which, incidental to normal oxidation in themolten steel and reoxidation as the steel solidifies, would formmanganese silicate inclusions whose characteristics are undesirable andwhich would also contain alumina as a result of the aluminum used fordeoxidation. It has been found that if steel containing manganeseandsilicon is continuously cast under conditions in which the oxygendissolved in the steel is present substantially only in that amountwhich is in equilibrium with the steel, the presence of calcium,sulfurand aluminum in particular quantities will avoid the formation of theundesirable silicates and alumina. Specifically, with calcium used inthe ladle and/or tundish for deoxidation and by employing an inertatmosphere surrounding the tundish-to-mold stream, so that the inertatmosphere exhibits substantially zero pressure of oxygen and carbonmonoxide as taught in the aforementioned copending application, thetundish-to-mold stream will be deoxidized to the desired degree and willcontain some residual and detectable calcium in solution (i.e., up to0.003 percent Ca). With this condition prevailing, and in the presenceof sulfur in the molten steel within the range of about 0.010 0.025percent and with the addition of aluminum within the range of about 0.010.08 percent, the non-metallic inclusions will be in the form ofmultiphase oxy-sulfides of aluminum, calcium and manganese which arerandomly dispersed in the solidified steel and which are of the size,shape and physical characteristics above noted.

As noted above, the aluminum is introduced at such a point or region andin such a way within the mold that uniform distribution in the moltensteel is assured. Consequently, it becomes a simple matter to controlthe speed of the motor as a function of the casting rate so that thedesired amount of aluminum is fed continuously to the steel. The uniformdistribution of the aluminum is also important in assuring the randomdispersion of the inclusions in the solidified steel and is thought alsoto be contributory to the small size of the inclusions.

The calcium is added in such amount as to provide a detectable residualtrace thereof in solution of up to 0.003 percent as determined by X-rayanalysis of the non-metallic inclusions.

Typical analysis for steel made according to the present invention isAISI 1,041 Carbon 0.36 0.44 percent, Manganese 1.35 1.65 percent,Phosphorus 0.035 percent max. and Sulfur 0.045 percent max. A typicalalloy grade is AlSl 4,140 Carbon 0.38 0.43 percent, Manganese 0.75 1.00percent, Phosphorus 0.035 percent max., Sulfur 0.04 percent max.,Silicon 0.20 0.35 percent, Chromium 0.80 1.10 percent and Molybdenum0.15 0.25 percent.

We claim:

1. In an apparatus for continuously casting steel, which includes atundish for receiving molten steel and having a discharge nozzle, avertically reciprocating mold aligned below said nozzle for receivingmolten steel therefrom, means for shrouding the tundish-tomold stream ofmolten steel, and means for maintaining an inert atmosphere in saidmeans for shrouding, the improvement comprising:

guide means carried by said mold so as to reciprocate therewith,

a supply of aluminum wire disposed remote from said mold and cooperatingwith said'guide means to supply a source of aluminum within said mold,and

means for feeding said aluminum wire into said mold at a predeterminedrate related to the rate of steel being introduced into said mold,

said guide means comprising a rigid tube attached to said mold and aflexible tube portion connected to said rigid tube and extending to saidsupply of aluminum wire,

the apparatus including a plate at the top of said mold forming a seatfor said means for shrouding said plate having an opening aligned withthe top opening of said mold and a groove intersecting such opening inthe plate, said rigid tube being received within said groove.

